Europeans brought a number of new diseases to New World. Smallpox was especially devastating to the Native populations.

Various European diseases are depicted in winter counts. Smallpox is shown in the Hunkpapa winter count for the years 1810, 1837, and 1844.

On Lone-Dog's winter count, smallpox is shown for 1801-'02, whooping cough is shown for 1813-'14, measles is shown for 1818-'19, and dropsy is shown for 1826-'27.

Corey writes:

The estimated population of Native Americans of North America (although nobody really knows for sure) was anywhere from 900,000 to 5 million before the Europeans arrived. In 1900 the population reached its nadir (lowest point), which was about 250,000—a mortality of 95%. The most important factor in the decline in the Native population was diseases that entered our country from the Eastern Hemisphere. The Europeans brought with them about 20 different diseases and of these they introduced smallpox, which killed off more than 95% of the population of Native Americans in North America. Smallpox reached its peak between 1800-1900. You can see many interpretations of smallpox on various winter counts and the women put cowry shells or elk’s teeth on their dresses to represent smallpox. You can see them today on the dresses of women traditional dancers.

References:

Hirschfelder.Arlene and Kreipe de Montano, Martha. The Native American Almanac. New York: Macmillan. 1993.

Thorton, Russell. Amerian Indian Holocaust and Survival: A Population History Since 1492. Norman, OK: University of Oklahoma Press. 1987.